Definitions of Managed Objects for the DS1, E1, DS2 and E2 Interface Types
obsoleted by
- rfc-3895 — Definitions of Managed Objects for the DS1, E1, DS2, and E2 Interface Types
obsoletes
- rfc-1406 — Definitions of Managed Objects for the DS1 and E1 Interface Types
Extracted elements (29)
A single MIB covers DS1, E1, DS2, and E2 because the various line disciplines are similar enough that separate MIBs are unwarranted. The design decision was made to closely align the MIB with objects that can generally be read from currently deployed devices rather than supporting all theoretically possible management objects.
dsx1IfIndex was deprecated in favor of using dsx1LineIndex equal to ifIndex, enabling proper use of the ifStackTable and DS0/DS0bundle MIBs. The ifStackTable is used for proxy scenarios (e.g., router proxying for a CSU shelf) to represent the association between interface pairs.
Performance statistics objects use PerfCurrentCount, PerfIntervalCount, and PerfTotalCount (all Gauge32 rather than Counter32) because these values can decrease — specifically when Unavailable Seconds occur across a 15-minute interval boundary, requiring retroactive adjustment.
The agent may choose to delay updates to statistics by 10 seconds to avoid retroactive adjustments required by the ANSI T1.231 unavailability definition. Appendix B sketches a 10-element delay-line approach that passes one-second statistics through a delay before updating counters.
Successive GETs of dsx1IntervalSESs and dsx1IntervalUASs may return differing values if the 10-second period leading to available or unavailable time crosses a 900-second statistics window boundary and the first GET occurs during the first few seconds of the new window.
The DS1 MIB uses ifType ds1(18) for DS1, E1, DS2, and E2 interfaces. The DS2 type is determined by examining ifSpeed or dsx1LineType rather than a separate ifType value. Interface types e1(19) and g703at2mb(67) are obsoleted by this MIB.
When an agent proxies for other devices, it may have missed collection of some statistics intervals. dsx1ValidIntervals reports the maximum interval number for which data is available, and dsx1InvalidIntervals reports the count of intervals within that range for which no data exists.
A linkDown trap shall be sent only after the agent has determined for certain that the unavailable state has been entered, but the timestamp on the trap shall reflect the time of the first UAS (i.e., 10 seconds earlier). A linkUp trap is handled similarly.
Agents supporting read/write access to dsx1LoopbackConfig must return inconsistentValue in response to a requested loopback state that the interface does not support.
dsx1NoAlarm must be set if and only if no other status flag is set in the dsx1LineStatus bitmap. If dsx1LoopbackState is set, the actual loopback in effect is determined from dsx1LoopbackConfig.
Performance parameters are accumulated in 15-minute intervals and up to 96 intervals (24 hours) are retained. Performance parameters continue to be collected when the interface is down.
The DS1 interface is unavailable from the onset of 10 contiguous Severely Errored Seconds (SES), or the onset of the condition leading to a failure. Once unavailable, all counters except UAS are frozen.
The far end cannot undo loopbacks set by a manager. A manager can undo loopbacks set by the far end. Both line and inward loopbacks can co-exist; a NoLoopback from the far end when an inward loopback was set by the manager leaves the inward loopback in place.
dsx1ChanMappingTable maps a DS1 or DS2 channel number on a parent DS3/E3 or DS2/E2 to an ifIndex, enabling representation of channelized hierarchies. The table is indexed by parent ifIndex and channel number.
dsx1Channelization is a read-write object with values disabled, enabledDs0 (DS1 channelized into DS0s), and enabledDs1 (DS2 channelized into DS1s). Setting this value causes the agent to create or delete ifTable entries for child interfaces.
dsx1LineCoding enumerates zero code suppression schemes: dsx1JBZS (Jammed Bit), dsx1B8ZS, dsx1HDB3, dsx1ZBTSI, dsx1AMI, and dsx1B6ZS (for DS2). E1 links use HDB3 or AMI; DS2 uses B6ZS.
dsx1LineStatus is a read-only bitmap (1..131071) representing simultaneous alarms and loopback states, including NoAlarm, RcvFarEndLOF, XmtFarEndLOF, RcvAIS, XmtAIS, LossOfFrame, LossOfSignal, LoopbackState, T16AIS, UnavailSigState, NetEquipOOS, RcvPayloadAIS, and Ds2PerfThreshold.
dsx1LineType enumerates supported framing formats: dsx1ESF, dsx1D4, dsx1E1, dsx1E1CRC, dsx1E1MF, dsx1E1CRCMF, dsx1Unframed, dsx1E1Unframed, dsx1DS2M12, and dsx2E2. The type determines bits-per-second capacity and interpretation of error statistics.
dsx1LoopbackConfig is a read-write object with values: dsx1NoLoop, dsx1PayloadLoop, dsx1LineLoop, dsx1OtherLoop, dsx1InwardLoop, and dsx1DualLoop (simultaneous Line and Inward). Agents must return inconsistentValue for unsupported loopback states.
dsx1LoopbackStatus is a read-only bitmap reflecting the actual current loopback state, distinguishing near-end (payload, line, other, inward) and far-end (payload, line) loopbacks, as well as the source (manager vs. remote). This is separate from dsx1LoopbackConfig, which represents desired state.
The DS1 Far End Group (dsx1FarEndCurrentTable, dsx1FarEndIntervalTable, dsx1FarEndTotalTable) collects performance statistics reported by the remote end via the ESF Facilities Data Link, mirroring the near-end structure.
The DS1-MIB defines managed objects for DS1, E1, DS2, and E2 interfaces, identified by ifType ds1(18). The MIB subsumes the former e1(19) and g703at2mb(67) types, which have been obsoleted.
The dsx1ConfigTable provides per-interface configuration including line type, line coding, loopback config, line status, signal mode, transmit clock source, FDL usage, line length, and channelization. It is indexed by dsx1LineIndex, which should equal ifIndex.
The dsx1CurrentTable, dsx1IntervalTable, and dsx1TotalTable hold performance statistics (ES, SES, SEFS, UAS, CSS, PCV, LES, BES, DM, LCV). Current covers the active 15-minute window; Interval covers the 96 prior 15-minute windows; Total covers the rolling 24-hour sum.
This document defines the DS1-MIB module registered under transmission(18) in the SNMP MIB tree (OID { transmission 18 }), covering objects for DS1, E1, DS2, and E2 interface management.
Several MIB objects have read-write or read-create access and could be misused. In particular, dsx1SendCode can cause a loopback or test pattern to be transmitted; dsx1LoopbackConfig can take an interface out of service; and dsx1LineStatusChangeTrapEnable controls trap generation. SNMPv1 community-based security is inadequate; SNMPv3 with authentication and privacy is recommended.
Far End Alarm (Yellow Alarm) state machine for ESF: declared when Yellow Alarm pattern occurs in at least 7 of 10 contiguous 16-bit intervals; cleared when pattern does not occur in 10 consecutive 16-bit intervals. D4 and E1 have different trigger conditions based on channel bit values.
Loss Of Frame Failure state: declared when OOF or LOS defect persists for T seconds (2 <= T <= 10); cleared when no OOF or LOS defects occur for T seconds (0 <= T <= 20). For E1, LOF is declared immediately upon OOF detection.
Unavailable Seconds state machine: interface enters unavailable state at onset of 10 contiguous SESs; exits when 10 contiguous seconds with no SESs occur. While unavailable, only UAS counter increments. Agents must retroactively adjust ES, BES, SES, SEFS, PCV, and DM counts when crossing the available/unavailable boundary near interval boundaries.